Depends on what kind of person you are! If you go halls of residence then its between dorchester, cranborne, lyme regis, purbeck, chesil. Corfe is pretty out of the way, in Poole. I'd say the halls stereotypes are as follows;
Purbeck - Sex drugs rock and roll etc, very social vibe, has matching tatty/generally damaged insides.
Cranborne - Lots of parties, often the location for predrinks, just been refurbished so is very nice also.
Chesil - Quiet house, usually. Not much goes on there, but the one and only time ive been inside was to a really huge party... Quite clean, modern, nice.
Dorchester - Most expensive, nicest, Seems like a tighter community due to its distance from the other 3-4 (only about a 10 minute walk but the others are basically next door)
Lyme Regis - Doesnt really have one that I (and others) seem to know of... Average halls i think!
Corfe - Quiet house AFAIK since its in poole, away from the main clubbing/studenty bit of bournemouth
If you're a social person with both crazy and sensible sides i'd recommend Dorchester or Cranborne, then decide out of the two whether you'd rather really luxurious halls, or basic but clean/modern halls that are closer to everything and the other halls.